1. Field of the Invention
The present invention relates to a monolayer metal gasket in which a monolayer metallic sheet is provided therein with gas holes and bolt holes allowing fastening bolts to fit in there, while extra thickness areas are arranged around the gas holes and the bolt holes to seal certainly a joint between confronting surfaces of, for example engine components.
2. Description of the Prior Art
A monolayer metal gasket of the type disclosed in Japanese Utility Model Laid-Open No. 139057/1981 is conventionally known to those skilled in the art. The monolayer metal gasket is composed of a metallic sheet of steel, copper, aluminum, and so on, which is turned over at the perimetral edges of the holes such as gas holes, coolant holes and others in the metallic sheet to thereby form cushions of arc in cross section.
Another prior monolayer metal gasket is disclosed Japanese Patent Laid-Open No. 200506/1996, in which there are provided folded constructions surrounding the gas holes and the bolt holes for sealing function, and beads of rubber-like substance arranged around the gas holes and the bolt holes for excessive compression-stopper function.
In most conventional multi-layered metal gaskets, the sheet with the folded construction serves for an intermediate plate regulating the thickness of the gasket. Because of rendering the metalworking of the folded construction much easier as well as the function of the intermediate plate, the sheet with the folded construction is of a thin sheet of about 0.1 to 0.2 mm in thickness. Thus, it becomes inevitable to overlay another sheet to support such thin sheet as stated earlier, for example, other additional intermediate plate on the primary intermediate plate. As a result, most multi-layered gaskets having at least three sheets introduce costly production requirements and become much complicated as a whole.
Moreover, in prior multi-layered metal gaskets installed between mating surfaces of, for example a cylinder head and a cylinder block of an engine, no special regard has been paid on the provision of any construction making it possible to suppress forcibly the warp or distortion that might occur in the mating surfaces at areas neighboring the bolt holes when the clamping force resulting from the tightening of the fastening bolts fitting in the bolt holes squeezes multi-layered metal gasket installed between the mating surfaces. Because of such condition as stated earlier, the multi-layered metal gaskets still undergo much deformation around the bolt holes and consequently the deformation occurring around the bolt holes in the multi-layered metal gasket affects negatively the areas around the gas holes to cause variations in clearance between the mating surfaces even around the gas holes. This makes it impossible to ensure the desired sealing stress with sufficient balance around the holes, which is enough to prevent leakage of pressure gases such as combustion gases from the joint around the gas holes.
A monolayer metal gasket in which only one metallic sheet is adapted between the confronting surfaces of the components to be jointed together is very simple in construction, compared with the multi-layered metal gasket stated earlier. Nevertheless, even such monolayer metal gasket made simplified in construction, the deformation or distortion occurring in the monolayer metal gasket around the bolt holes when the tightening of the fastening bolts clamps together the mating surfaces of the confronting components affects negatively the sealing stress acting on the mating surfaces around the gas holes. Thus, it will be worthwhile limiting an amount of distortion in the gasket to thereby make the sealing stress between the mating surfaces much more stable.
The present invention has as its primary object to provide a monolayer metal gasket comprising a single metallic sheet made therein with gas holes and bolt holes in which fastening bolts fit, wherein the metallic sheet is provided with extra thickness constructions around the gas holes and the bolt holes, one to each hole, the extra thickness constructions being made larger in thickness than a major area of the metallic sheet to ensure a desired sealing stress with sufficient balance around the gas holes where pressure gases such as combustion gases flow, thereby preventing leakage of pressure gases such as combustion gases through between the mating surfaces of the engine components.
The present invention is concerned with a monolayer metal gasket comprising a single metallic sheet made with a gas hole and a bolt hole through which a fastening bolt is adapted to pass, a first extra thickness formed around the gas hole and made larger in thickness than the metallic sheet, and a second extra thickness formed around the bolt hole and made larger in thickness than the metallic sheet, wherein the first extra thickness is provided by turning back a part of the metallic sheet on a major flat of the metallic sheet, with leaving a space open between them, while the second extra thickness is provided by folding back a part of the metallic sheet on the major flat of the metallic sheet to make a closely layered construction.
In accordance with one aspect of the present invention, a monolayer metal gasket is disclosed wherein the first extra thickness is composed of a first base part extending around the gas hole integrally from a major flat of the metallic sheet, and a first folded part integral with the first base part and turned back on the first base part, with leaving the space between them.
In accordance with another aspect of the present invention, a monolayer metal gasket is disclosed wherein the second extra thickness is composed of a second base part extending around the bolt hole integrally from a major flat of the metallic sheet, and a part overlaid on the second base part into the closely layered construction.
In accordance with another aspect of the present invention, a monolayer metal gasket is disclosed wherein the overlaid part is a second folded part extending integrally from the second base part and turned back around the bolt hole.
In accordance with another aspect of the present invention, a monolayer metal gasket is disclosed wherein the overlaid part is a part prepared independently of the metallic sheet and arranged around the bolt hole.
In accordance with a further another aspect of the present invention, a monolayer metal gasket wherein the overlaid part is a washer.
In accordance with another aspect of the present invention, a monolayer metal gasket is disclosed wherein the overlaid part is made of a lug protruding integrally out from the major flat of the metallic sheet and made therein with a cut hole, with leaving an annular part, the lug being turned back in such a way to align the cut hole with the bolt hole whereby the annular part surrounds the bolt hole.
In accordance with another aspect of the present invention, a monolayer metal gasket is disclosed wherein the second extra thickness has a thickness twice as much as the major flat of the metallic sheet.
In accordance with another aspect of the present invention, a monolayer metal gasket is disclosed wherein the major flat of the metallic sheet has a thickness ranging from 0.2 mm to 0.8 mm.
In accordance with a further aspect of the present invention, a monolayer metal gasket is disclosed wherein the metallic sheet is overlaid with a shim plate at an area between any adjacent gas holes.
The monolayer metal gasket constructed as stated earlier is made of a single metallic sheet having elasticity. In addition, the first extra thickness around the gas hole is formed in a folded construction in which a folded part is turned over the major flat of the metallic sheet not to form an closely overlaid construction but to leave the space between them to afford the resiliency at the first extra thickness.
In contrast, the overlaid part in the second extra thickness around the bolt hole comes in overall close engagement with the major flat of the metallic sheet to form a closely layered construction of nearly rigid body little to be deformed even when the monolayer metal gasket is squeezed.
With the monolayer metal gasket of the present invention, the first extra thickness has the elasticity by virtue of the space whereas the second extra thickness is formed in nearly rigid body little to be deformed.
When the clamping force that results from the tightening of the fastening bolt squeezes the monolayer metal gasket installed between the mating surfaces of the components to be sealed together, the second extra thickness of nearly rigid body is seldom subject to deformation, and therefore the amount of tightening, ranging from a first status where the axial force of the fastening bolt begins forcing the gasket to a second status where the tightening of the fastening bolt is made completed, may be controlled to a preselected desired amount of tightening. Thus, the clearance around the bolt hole between the mating surfaces may be regulated well to a preselected distance. The second extra thickness also serves for the sealing function around the bolt hole.
With the monolayer metal gasket of the present invention, the first extra thickness, when squeezed between the mating surfaces, serves for the seal around the gas hole by virtue of the elasticity in itself, while the second extra thickness serves to regulate the clearance between the mating surfaces of the components to a preselected distance. Even around the gas hole, the clearance between the mating surfaces is adjusted depending on the preselected distance regulated at the second extra thickness. This results in reducing the variation in sealing stress around the gas hole, thereby realizing the desired sealing stress with preferred balance.
As the second extra thickness regulates well the clearance between the mating surfaces to the desired distance, the clearance between the mating surfaces around the gas hole is also adjusted according to the preselected distance regulated at the second extra thickness whereby the sealing stress around the gas hole is reduced in variation to be made stabilized. This contributes to the sealing stress balanced well around the gas hole. Varying the relation in thickness between the first extra thickness and the second extra thickness may carry out control of the sealing stress around the gas hole.
Moreover, since the monolayer metal gasket of the present invention is principally made of a single metallic sheet having elasticity, the monolayer metal gasket may be made simple in construction and inexpensive in production cost.